[AF] Use account id hash as key for wallet sync transport opt-in pref.

Bug: 907929
Change-Id: I6cc9d7a908010c204fc8060802c7ee453363ffa3
Reviewed-on: https://chromium-review.googlesource.com/c/1349455
Commit-Queue: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Fabio Tirelo <ftirelo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612769}
4 files changed